The present invention relates to Bipolar Junction Transistors (BJTs) using InAs-based or InSb-based semiconductor materials, and in preferred embodiments describes Heterojunction Bipolar Transistors (HBTs).
Bipolar Junction Transistors, of course, remain among the most widely used semiconductor devices. Heterojunction Bipolar Transistors (HBTs) find use in a number of high power, microwave applications, including cellular telephones, telecommunication equipment, radar equipment, etc. Compared with other devices which operate in the microwave range, such as Gallium Arsenide (GaAs) Field Effect Transistors (FETs), HBT devices realize higher gain amplification in the microwave range. However, as is generally known, an HBT device operates at a relatively high current density, and thus prior art HBTs have inevitably generated heat at a relatively high rate with respect to the device""s area. In order to operate such a prior art HBT, special steps have sometimes been taken to conduct the heat generated at a PN junction formed on a surface of a substrate of an HBT away from the device""s substrate. One prior art technique for releasing internally generated heat from an HBT is discussed in U.S. Pat. No. 5,831,337 of Sato.
Both Single Heterojunction Bipolar Transistors (SHBTs) and Double Heterojunction Bipolar Transistors (DHBTs) are known in the prior art. Generally speaking, in a SHBT, only the emitter has a wider bandgap than the bandgap of the base, while in a DHBT, both the emitter and the collector have a wider bandgap than that of the base. Indium Phosphide (InP) is commonly used as a substrate material upon which group III-V semiconductor devices are formed from layers of semiconductor materials such as AlInAs and GaInAs. While such devices have high speeds desirable for microwave applications, they tend to consume a fair amount of power, which gives rise to the heat generation problems noted above.
As such, there is a continuing need to reduce the power consumption of HBT devices, and the present invention addresses that need. Moreover, there is a continuing need for devices which can operate at still higher frequencies and the present invention addresses that need as well.
The present invention relates to a novel class of BJTs which use p-type InAs. In the preferred embodiments, such a BJT takes the form of an HBT employing InSb-based compositions, particularly InPSb, as a wide-bandgap material. One preferred SHBT embodiment of the invention has an n-type InPSb emitter, p-type InAs base, and n-type InAs collector, while a preferred DHBT embodiment has an n-type InPSb emitter, p-type InAs base, and n-type InPSb collector. These devices may be grown lattice-matched to an InAs substrate. Devices according to the present invention may also be grown lattice-matched on a GaSb substrate by adding Sb to the materials. Thus, other preferred embodiments have an n-type InPSb emitter, a p-type InAsSb base (preferably InAs0.91Sb0.09), and an n-type InAsSb collector (for a SHBT) or an n-type InPSb collector (for a DHBT). These 6.1 xc3x85 compound semiconductor materials have superior transport properties that result in BJTs with very high speed. The preferred embodiments use these 6.1 xc3x85 compounds in combinations that provide opportunities for greatly reduced power consumption. Consequently, devices according to the present invention are particularly useful for digital signal processing applications.